How does Card Sharing work??

How does Card Sharing work??
I have Dreambox DM500 and something called 'Newcamd-Betad6.10b' on it. This is directly connected to my ADSL router for internet access.
I had paid someone to give me access to paid channels. I don't know exactly what he had done.
I understand Newcamd has something to do Cardsharing. I am just trying to understand what he would have done to get it working so I can do it myself in the future.

Lately, when my TV goes blank, and I have to call up the Sat guy. He apparently does something and I can watch TV normally, what is it that he does??